The present invention relates to a system for automatic and consistently accurate feeding of flat sheets, for example sheets of paper, from a pile of sheets loaded into a machine which takes those sheets one by one, for instance a collator.
In the market two basic sheet feeding systems exist: suction feed systems and friction feed systems. Suction fed systems perform well, but are costly and space-consuming; furthermore, such systems call for delicate adjustment of air and vacuum and an incorrect feed, such as a double feed, is only detected after the sheets have moved away from the pile, which can frequently cause paper jams and machine stoppages and requires special intervention by the operator. Further, the rubber used in the suction means will dry and perish leading to frequent replacement.
Friction feed systems call for a constant pressure on the sheet by a feeder pad or roller. The adjustment of the pressure is critical and this means that the range of papers that can be handled by friction feed systems is narrow and it is generally not possible to feed very thin and/or delicate papers or very heavy and slippery material.
Whatever their method of feeding, the known systems are all sensitive to the variable parameters of a given pile of sheets to be fed: physical dimensions, weight, density, humidity, a tendency to stick together, static electricity, all of which can vary within the same pile. In particular with sheets of paper, it should be noted that the consumption of paper shows a continuing upward trend in the use of delicate papers such as self-copy paper.
Known friction feed systems are generally incapable of operating with these types of paper and suction feed systems operate with difficulty.